Technical Field
The present invention disclosure relates generally to a method and apparatus for separating products based on size. More particularly, the disclosure herein describes an improved separation apparatus with a novel separation screen having openings of fixed, but non-uniform sizes arranged in a size-based gradient. Depositing a feed stream onto a selected region of the separation screen separates the feed stream into product streams with a desired size distribution.
Background
A vibratory screener, also referred to herein as a sifter, is a separation apparatus that can separate a feed stream into two or more product streams, each having particles of different sizes. There are two predominant types of vibratory screeners: centrifugal screeners and longitudinal screeners. Currently existing centrifugal screeners use one or more circular screens to separate a feed stream into two or more product streams based on size of particles that form the feed stream. In particular, separation is achieved by vibrating a separation screen on which the feed stream has been deposited. Larger particles unable to pass through the holes in the separation screen are removed from the centrifugal screener as a retained product stream. Smaller particles of the feed stream fall through the holes in the screen during agitation are often collected as a pass-through product stream.
A longitudinal screener uses one or more rectangular screens to separate a feed stream into two or more product streams. The particles of a feed stream are deposited onto the upstream end of a separation screen and then vibrated to cause the particles of the feed stream to travel down a length of the separation screen. Larger particles unable to pass through the holes in the separation screen are removed at a downstream end of the separation screen as a retained product stream. Smaller particles of the feed stream fall through the holes in the screen during agitation and are often collected as a pass-through product stream.
To change the size distribution of particles in the product streams, an installed separation screen would need to be replaced with another screen having uniform holes of a different size to achieve the desired separation. Alternatively, one or more additional screens may be added in series to change the size of particles in the product streams. However, this is time consuming because it requires a technician to take the vibratory screener apart and make the necessary changes. The production line needs to be shut down temporarily, which reduces throughput and profit.